Pressure would have to be maintained until the material cures. Which would work for resin, just heat the pressure vessel to activate, and let it sit until solid. I guess there might be some oddness about heating a pressure vessel, just make sure it's good for it.
Then you have trapped bubbles under pressure, which will eventually diffuse back to ~atmospheric depending on material properties, though that could take very long indeed. Well, at least if they're under pressure, they'll have higher breakdown voltage, which is a good thing. Although they'll be smaller too, but, that means more E-field, which still works out. Preferable to remove voids of course, but una-void-able (ha) ones under pressure is better than not.
It wouldn't work so well for varnish, where the pressure will reduce evaporation rate, and that's if you have ventilation in the chamber at all (say, a cold trap off to the side?).
Tim